This invention relates to an instrument for the placement of a stent in a body canal and particularly to an instrument for the deployment or retraction of a self-expanding stent.
Tubular prostheses for transluminal implantation in body canals, for example blood vessels, for the purpose of repair or dilation are known in the art. These prostheses, referred to herein as stents, may be tubular elements which are non-extendible or extendible (i.e. adapted to extend longitudinally), or they may be self-expanding in the transverse direction.
A typical self-expanding stent is disclosed in U.S. Pat. No. 4,665,771, which stent has a radially and axially flexible, elastic tubular body with a predetermined diameter that is variable under axial movement of ends of the body relative to each other and which is composed of a plurality of individually rigid but flexible and elastic thread elements defining a radially self-expanding helix. This type of stent is known in the art as a "braided stent" and is so designated herein. The disclosure in U.S. Pat. No. 4,665,771 is incorporated herein by reference.
Placement of the stent according to U.S. Pat. No. 4,665,771 in a body vessel is achieved in one embodiment by a device which comprises the use of a piston or, in another embodiment, by use of latch means to push the stent forward.
U.S. Pat. No. 4,768,507 discloses a stent insertion apparatus which includes an inner core member with a spiral groove formed on its outer surface, which groove cooperates with an outer sheathing to form a spiral cavity adapted to contain an expandable coil stent. The coil stent is held in a radially compressed state within said spiral cavity by exerting a radial outward force on the outer sheath. The outer surface of the inner core member is slidably mounted within the hollow outer sheath cylinder so that the spiral cavity is adapted to contain only the coil stent for which it is designed. U.S. Pat. No. 4,743,152 discloses a device for implantation of a substantially tubular, radially expandable prosthesis including in combination said radially expandable prosthesis surrounding and concentric with a flexible probe and means for maintaining said prosthesis in a radially contracted state and for releasing said expandable prosthesis, wherein said means for maintaining and releasing the prosthesis comprises a hose concentrically surrounding said probe with one end of said hose being connected to the probe, the hose being folded inside itself, a double-walled section of said hose formed by said hose being folded inside itself, said double-walled section radially surrounding the prosthesis, a fluid-tight chamber provided between and defined by said probe and said hose, means for introducing and pressurizing a fluid in said chamber to reduce contact pressure and friction between said double-walled section of the hose, the prosthesis being released from the hose by axial relative movement of said one end of the hose with respect to an opposite end of said hose, said opposite end of said hose connected to an element of said device. The requirement that a chamber formed by a folded hose or outer sheath requires to be inflated with a pressurized fluid makes the device cumbersome and awkward to operate.
It has now been found that a self-expanding braided stent, such as that disclosed in U.S. Pat. No. 4,665,771, may be not only deployed into a body canal but also retracted back into the outer sleeve of a placement instrument which is simple, reliable and inexpensive if said instrument has the configuration and features as hereinafter described.